I think level-sync should be optional. I like the concept of the idea and I wouldn't mind doing all content at the level that it's meant to be done at at least once. As others have pointed out, sometimes I just want to bum rush content on a higher level and I shouldn't be restricted in doing that. I know people in my LS are strongly against forced level capping for content and it would probably be a deal breaker for them even playing ARR.

The gear/ability scaling would have to work well too. I don't want to have to carry 10 sets of equipment around to be able to participate in level capped content like in CoP.

I don't think we have enough information to speculate which way it's going to go yet. All we know is that "there's level sync". Let's wait for Yoshi-P to give us the official word before we bring out the torches and pitchforks.